corresponds to the sensation, I term its matter; but that which
effects that the content of the phenomenon can be arranged under
certain relations, I call its form. But that in which our sensations
are merely arranged, and by which they are susceptible of assuming
a certain form, cannot be itself sensation. It is, then, the matter
of all phenomena that is given to us a posteriori; the form must lie
ready a priori for them in the mind, and consequently can be
regarded separately from all sensation.

I call all representations pure, in the transcendental meaning of
the word, wherein nothing is met with that belongs to sensation. And
accordingly we find existing in the mind a priori, the pure form of
sensuous intuitions in general, in which all the manifold content of
the phenomenal world is arranged and viewed under certain relations.
This pure form of sensibility I shall call pure intuition. Thus, if
I take away from our representation of a body all that the
understanding thinks as belonging to it, as substance, force,
divisibility, etc., and also whatever belongs to sensation, as
impenetrability, hardness, colour, etc.; yet there is still
something left us from this empirical intuition, namely, extension
and shape. These belong to pure intuition, which exists a priori in
the mind, as a mere form of sensibility, and without any real object
of the senses or any sensation.

The science of all the principles of sensibility a priori, I call
transcendental aesthetic.* There must, then, be such a science forming
the first part of the transcendental doctrine of elements, in
contradistinction to that part which contains the principles of pure
thought, and which is called transcendental logic.